The detection of vehicle wheel axles is of importance in numerous applications. For instance, travel on a specific traffic surface can be reliably determined from the detection of a wheel axle, e.g. for border crossing or for activation of specific actions such as triggering an alarm, switching on a lighting system, opening a barrier, taking a photograph for monitoring purposes etc. Modern traffic payment systems are also frequently directed towards the number of axles of vehicles to assess charges, so that the detection of wheel axles can also be an important basis for road toll or parking fee systems.
A wide variety of systems are currently used for the detection of wheel axles, such as induction loops embedded into the roadway, light barriers just above the roadway or radar or laser scanners over the roadway, which also detect wheel axles as part of vehicle contour recognition. What all the known systems have in common is that they are extremely expensive, for example, induction loops require the surface of the roadway to be opened up, light barriers require installations on both edges of the roadway and are ineffective on roads with multiple lanes, and radar or laser scanners are structurally complex and costly.